Field of the Invention
The present invention relates to image display apparatuses such as a head-mounted display (HMD) and a projector
Description of the Related Art
Image display apparatuses each having a display optical system that magnifies an original image formed on an image forming element such as a liquid crystal element and presenting a magnified observation image to an observer are desirable to be compact and have a wide angle of view. In particular, an HMD to be mounted on a head of the observer observing the observation image through his/her right and left eyes includes right and left paired image forming elements and right and left paired display optical systems, so that a decrease in size thereof is important.
Japanese Patent Laid-Open Nos. 10-153748 and 2000-105338 each disclose an image display apparatus using as a display optical system an eccentric prism whose reflective surfaces having optical powers are eccentrically arranged.
Furthermore, U.S. Pat. No. 5,861,995 discloses a holding structure for positioning and holding, in an image display apparatus, a prism constituting a display optical system.
An increase in angle of view of the display optical system in the HMD increases a maximum optical effective area (a required area of an optical surface having an optical function), which results in an increase in size of the display optical system. The increase in size of each of the right and left display optical systems causes a physical interference therebetween.
A person's interpupillary distance, which is a distance between person's right and left eyes, is about 60 mm in general. A interpupillary directional width of each display optical system, which is its size in a interpupillary direction in which the right and left eyes are arranged, is necessary to be smaller than at least the person's interpupillary distance.
Moreover, when the image display apparatus is provided with an interpupillary distance adjustment mechanism for adjusting a distance between the right and left display optical systems so as to match that distance to an observer's interpupillary distance, the interpupillary directional width of each display optical system defines a smallest adjustable distance between the right and left display optical systems, so that the interpupillary directional width is desirable to be as small as possible.
However, an optical element such as a prism constituting each display optical system is necessary to have a connection portion connected to a holding portion (or supporting member) in the image display apparatus such that the optical element is held at a fixed position in the image display apparatus. If the connection portion protrudes, in the interpupillary direction, further outside than a maximum width of an optical portion necessary for image observation in the optical element, an interpupillary directional space necessary for arranging each display optical system is increased by an amount corresponding to the protrusion, which results in an increases in size of the entire image display apparatus and in a restriction in interpupillary distance adjustable amount.